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Investments - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
3 Months Ended 9 Months Ended
Sep. 30, 2013
Sep. 30, 2012
Sep. 30, 2013
Sep. 30, 2012
Sep. 30, 2013
Blackstone's Net Assets
Sep. 30, 2013
Consolidated Blackstone Funds
Dec. 31, 2012
Consolidated Blackstone Funds
Investment [Line Items]              
Investments           $ 506.3 $ 500.5
Threshold of individual investment fair value to net assets, percentage         5.00%    
Recognized net gains related to equity method investments $ 71.3 $ 81.4 $ 282.6 $ 125.4